In existing barcode scanning systems, a laser beam is scanned over a barcode and the light reflected therefrom is captured and analyzed for information content. The reflected light increases and decreases as the laser scans over light and dark sections of the barcode, respectively. When a barcode scanner operates in an environment with relatively large ambient light, the signal can get lost or distorted by the ambient light. Specifically the ambient light is also amplified by the signal amplifier, which can have a large dynamic range. The ambient light can overshadow the signal, often making it difficult to decode the signal.
One known prior art solution to this is to differentiate the reflected light captured prior to the final amplification. Since the frequency at which the reflected light from the barcode changes is significantly greater than the frequency at which the ambient light increases and decreases, differentiation can reduce the effect of the ambient light. Or, put in another way, the ambient light will have a much lower value of derivative, than the reflected light from the barcode signal.
FIGS. 1 and 2 show a block diagram of an existing digitizer circuit, with FIG. 2 representing the internal components of digitizer 101 of FIG. 1. In the arrangement of FIG. 2, the signal is initially compared with noise elimination levels that are larger than the noise and lower than the barcode signal. These outputs 201 and 202 are then fed to logic gates 203 and 204 while the first differentiated signal received is differentiated again by differentiator 205. The process of the existing digitizer shown in FIG. 2 is demonstrated in FIGS. 3-9, where the wave forms at the output of the various analog and digital components of FIG. 2 are indicated. In the end, FIG. 9 shows that the digitized signal is emitted from a flip flop 210.
Although the above prior technique provides some improvement of performance in environments of strong ambient light, the use of a derivative to reduce the impact of ambient light is often not enough. As a result, the signal can be misread and incorrectly decoded.
In view of the foregoing, there exists a need in the art for a system that can better eliminate the effects of ambient light on the barcode scanning system.